Novel, multilayer coupled-line structures and their circuit applications

Presented are characteristics of new (or described in the literature but not in detail) symmetric and asymmetric coupled-line structures which are of use in the design of quasi-ideal multilayer microstrip and coplanar directional couplers as well as other coupled-line passive components for monolithic and hybrid microwave integrated circuits. In several designs of tightly and weakly coupled multistrip lines, the coupling coefficient can be achieved in a large range of values, enabling at the same time their quasi-ideal realisation for a given dielectric stratification of the structure. This property allows the design of high-performance multisection coupled-line passive circuits, which are very sensitive to how much the coupling coefficients for individual coupled-line sections differ from the values determined by the circuit synthesis methods. The investigated structures have been used in the design and practical realisation of the following integrated circuits: single- and multi-section coupled-line directional couplers, filters, phase shifters and power dividers, as well as coupled-line compensated baluns, non-reflective multiple pin-diode attenuators/DPDT switches, compact multidimensional Butler matrices, and broadband in-phase antenna array feeding networks. We include the design data and experimental results for most of the circuits we describe. The paper presents the results of the authors´ research into the properties and applications of new microstrip and coplanar lines from the period of the past few years. Some of the most recent results (not yet published) are also presented